1. Field of the Invention
The invention relates to a process for adjusting a motor vehicle part between at least two positions, and a drive device for a motor vehicle part which can be adjusted between at least two positions.
2. Description of the Related Art
DE 43 21 264 A1 discloses a generic process and generic drive device in which an electric motor drives a motor vehicle window pane. By means of two Hall sensors which are offset by 90 degrees and which interact with a magnet located on the motor shaft a signal is produced from which the instantaneous period duration of a motor revolution and thus the instantaneous motor rpm are determined at each time at which one such signal enters a control unit for controlling the motor. As soon as the instantaneous rpm change resulting from the difference of two successive rpm measured values exceeds a stipulated threshold value the motor is reversed in order to release a possibly pinched article.
DE 195 11 581 A1 discloses a similar drive device in which the threshold value is variably chosen depending on the position, and a memory for certain positions of the adjustment path, and storing the speed change sampled in an earlier run between two adjacent positions in order to compute the shut-off threshold for the speed from a function of position depending on the last currently determined position and the speed.
DE-OS 29 26 938 discloses acquiring the motor rpm in a sliding roof drive at uniform time intervals, finding the differences of successive values, adding these differences to one another when they are larger than a predetermined threshold value, and triggering the shut-off or reversal of the motor as soon as the added sum exceeds a predetermined threshold value.
DE 43 12 865 A1 discloses a drive device for a motor vehicle window which samples the motor rpm by means of two Hall detectors, and, which when a threshold is exceeded for the relative change of rpm, reverses the motor. In doing so, the threshold value is continually re-computed depending on the sampled motor voltage and the ambient temperature which is determined by a temperature sensor on the motor. The status/operating times of the motor are then considered in order to draw conclusions about the ambient temperature from the motor temperature.
DE 196 18 219 A1 discloses determining the rpm threshold or the rpm change threshold of the motor, from which reversal of the motor takes place, by determining the position-dependent rpm data of a reference run taken place beforehand and depending on the position of the cover for a sliding roof drive.
EP 0 422 388 A1 discloses pinching protection for an adjustable motor vehicle part in which the first derivative of the drive motor torque is added over part of the range of motion of the adjustable motor vehicle part, a boundary value for the sum being used to shut off the drive motor.
U.S. Pat. No. 5,278,480 describes a learning program for a device for opening and closing a garage door.
DE 40 00 730 A1 discloses pinching protection for an adjustable motor vehicle part by the monitoring of the motor rpm or the first derivative of the motor rpm such that pinching will be recognized. The characteristics of the individually used motor, optionally with consideration of the inherent heating of the motor, are determined by connecting the motor to a completely assembled part and then exposing the part to a defined load moment from which the motor rpm is determined. The disadvantage in this pinching protection is that only adaptation of the entire system comprising the motor characteristic, the motor temperature, and the resistance to movement of the adjustable motor vehicle part is possible. This results in a certain amount of inaccuracy in recognition of pinching.
The disadvantage in the above generic systems, which sample the rpm, is that due to individual fluctuations of the characteristics of the motors used, the assignment of the measured rpm to the corresponding motor torque, i.e. the corresponding force acting on the adjustable motor vehicle part, is subject to these random fluctuations; this results in inaccuracies in the determination of a case of pinching.
The object of this invention is to provide a drive device for a motor vehicle part which can be moved between at least two positions and a process for adjusting a movable motor vehicle part between at least two positions, which will provide better accuracy in the determining whether a case of pinching has been encountered.
In this approach, there is an improvement when fluctuations in the individual motor characteristic of the electric motor utilized can be compensated for such that an accurate determination of the motor torque and thus of the force acting on the adjustable motor vehicle part can be determined, the result of which is that the accuracy in determining whether a case of pinching has occurred can be improved.
In a preferred embodiment, the instant input of each pulse signal on the control unit is measured, from at least some of the previously measured instants one value at a time for the change of the motor rpm is determined, and from each value of the rpm change, when multiplied by a proportionality factor, a force change value is determined which is then used when the value is determined for the instantaneous force acting on the moveable motor vehicle part.
The proportionality factor is chosen as a function of the motor characteristic.
Preferably, the motor characteristic is determined for at least one motor voltage before startup, i.e., without the driven motor vehicle part is assembled, and at a fixed motor voltage, and more preferably two pairs of values of rpm and torque are measured.
Furthermore, the proportionality factor is preferably chosen as a function of the motor temperature, with the motor temperature preferably being estimated by the ambient temperature and the duration of motor operation being measured.
Two embodiments of the invention are detailed below using the attached drawings.